1. Field of the Invention
The inventions relate to a sheath or catheter that has an expandable distal end.
2. Description of Related Art
In many minimally invasive medical procedures, a sheath may be placed in a blood vessel to gain access to a site within a body for a diagnostic or therapeutic procedure. Sheaths and catheters are used as conduits to pass objects, such as surgical instruments, medical implants, or biological matter e.g., clots, tissue samples, or other matter. It is generally desirable to minimize the outer diameter of the sheath and maximize its inner diameter. A small outer diameter is desired to minimize the size of the wound at the insertion site. A smaller outer diameter also provides less disruption to the circulatory pathway. Within the constraint of the desired small outer diameter, the inner diameter of the sheath is designed to be as large as possible for the objects to pass through it. Since the outer diameter is preferably minimized and the inner diameter is preferably maximized, the wall of the sheath is relatively thin. The thin wall of the sheath can in some cases lack sufficient strength for insertion into a blood vessel or other circumstances in which the sheath may be subjected to longitudinal or circumferential forces. Thus, materials commonly selected for the construction of sheaths typically have high stiffness or rigidity.
Objects, such as surgical instruments, medical implants, or biological matter may require removal from the body or repositioning within the body. An object that is to be removed may be a temporary implant which has performed the desired diagnostic or therapeutic function. Alternatively, an object may be a permanent implant that requires removal for some other reason. Sometimes objects need to be repositioned in the body after their implantation. One way of retrieving the object for removal or repositioning is to pull the object back into a sheath (or push the sheath around the object) so that the object is disposed within the sheath. Once retrieved into the sheath, the object can be repositioned and redeployed at a desired delivery location, or removed completely from the body. Some objects have different delivery and deployed configurations. Objects that have an enlarged deployed configuration must be compressed or transformed to a reduced profile configuration in order to be reintroduced into a sheath.
In some cases, such an object may not collapse into its reduced profile configuration completely. In other cases, the object may have physical features or unique geometries, e.g., edges, protruding arms, etc. that require careful orientation and manipulation during removal or a repositioning procedure. These features can cause difficulty in retrieving such an object back into the sheath. Furthermore, this difficulty may be compounded by the material choice for and construction of the sheath. The high stiffness or rigidity of the sheath material may make the withdrawal of an object more difficult because such sheath will not expand to accommodate an object that can not be completely reconstrained to its original reduced profile. The thin wall of such a sheath may lack of sufficient strength and, therefore, may kink, bend or fold as an object is pulled into the distal end of the sheath. Moreover, the physical features or unique geometries of an object may be caught by the distal edge of the sheath, thereby dragging the edge inward and tearing the sheath or folding the sheath inward. This can result in an even smaller inner diameter and, therefore, increased difficulty of retrieving.